Evaluate Azvudine in Preventing SARS-Cov-2 Infection in Household Contacts of Covid-19 in China

Inclusion Criteria: 1、18-65 years old at the signing of informed consent. 2、Household contacts of individual with symptomatic COVID-19. Symptomatic COVID-19 cases (index case) to be identified as those symptomatic and recently tested (rapid antigen test or RT-PCR) positive for SARS-CoV-2 and must fulfill the following criteria 1) collection of the first positive SARS-CoV-2 test sample less than 24 hours before randomization, 2) have at least one symptom attributable to COVID-19. 3、RT-PCR test negative (with nasopharyngeal \[NP\] swab samples) OR rapid antigen test negative at the time of screening and without any suspicious COVID-19 symptoms within 2 weeks before randomization. 4、Subject expects to be living in the same household with the symptomatic COVID-19 cases during the whole study period. Exclusion Criteria: 1. Subject with a history of SARS-CoV-2 vaccinations within 1 months before randomization. 2. Subject with a history of SARS-CoV-2 infection within 6 months before randomization. 3. With any serious infection requiring systemic anti-infective therapy within 14 days before randomization. 4. Allergic to the investigational agent or any components of the formulation. Pregnant or breast-feeding women. 5. Women of childbearing potential who are unwilling to practice highly effective contraception during the study, and for at least 6 months after the study; Sexually active men who are unwilling to use medically acceptable birth control during the study period. 6. Have other conditions not suitable for inclusion as judged by the investigator.